Ageing doctor keeps arguing, you heard (7,2)
I believe the answer is:
growing up
'ageing' is the definition.
Although both the answer and definition are present participle verbs, I can't see how one could define the other.
'doctor keeps arguing you heard' is the wordplay.
'doctor' becomes 'GP' (general practitioner).
'keeps' indicates putting letters inside (inserted letters are kept inside).
'arguing' becomes 'rowing' (I've seen this before).
'you heard' becomes 'U' (homophone of 'you').
'rowing'+'u'='rowingu'
'gp' placed around 'rowingu' is 'GROWING UP'.
Can you help me to learn more?
(Other definitions for growing up that I've seen before include "getting bigger?" , "showing more mature attitude" .)